Silicone medical device components have the advantages of high flexibility and biostability. However, they also possess the disadvantage of being relatively weak in their mechanical properties such as tensile strength and abrasion resistance. Frequently a surface layer of a high abrasion resistant material is required above a substrate of a silicone device. Polyurethanes offer that high abrasion resistance and other good mechanical properties.
However, some of the properties of polyurethanes make the combination of silicone and polyurethane components difficult.
Most commercial polyurethanes are not biostable and tend to break down under in-vivo conditions in long term implantation.
Biostable polyurethanes are disclosed in WO92/00338, WO98/013405, WO98/54242, WO99/003863, WO99/050327, WO00/64971 and WO2007/112485 including ELAST-EON 2 (AORTECH BIOMATERIALS, Victoria, Australia) which is a polyurethane having a soft segment based on 80 wt % of a hydroxyl terminated polydimethylsiloxane (PDMS) and 20 wt % of a polyether polyol specifically polyhexamethylene oxide (PHMO). These polymers are stable under in-vivo conditions and can been used for many long term implantable applications.
Bonding of silicone based components to polyurethane based components has been tried using several methods. Treating the surface of silicone with a primer, use of glues and plasma treatments have been employed and these methods deliver a bond with certain degree of adhesiveness. However, in many applications the bond has proven to be inadequate. The bonding of most materials to silicone is a challenge due to the low surface energy of silicone. In fact silicone sprays are used in mould releases and moulds can be constructed from silicones to provide good release of mouldings.